RFID systems are fast becoming the identification medium of choice due to the speed and accuracy with which a user can identify the quantity and type of tagged items present. RFID also holds promise as a medium for gathering information about tagged items and their environments, such as temperature history profiling. However, one major drawback of RFID when used in the supply chain to monitor, for example a temperature history profile of goods in transit, is that the user must have an interrogator present in order to read the temperature history profile. Consider the following.
Many materials in use in commerce, medicine, and other areas are perishable. That is, the materials have a tendency to deteriorate with time, and this tendency to deteriorate is often accelerated by exposure to higher temperatures. This tendency to deteriorate is often designated as a material's “stability”. A material that deteriorates slowly in response to higher temperatures over long periods of time is said to have a “high stability”. By contrast, a material that deteriorates quickly in response to higher temperatures is said to have a “low stability”.
Examples of deterioration includes spoilage in the case of biological materials, loss of potency in the case of drugs, loss of chemical reactivity in the case of chemicals, or alternatively formation of unwanted contaminants, etc. Excessive deterioration eventually results in the material in question being rendered unfit to use, or even rendered dangerous. Thus for commerce, medicine, and other areas, the rapid detection of materials rendered unfit to use by an unacceptable thermal history is very important.
Additionally, there are alternative situations where a material must undergo a certain minimal thermal history before it becomes fit for use. There are many materials, and material treatment processes, commonly used for construction, manufacturing, food preparation, and pharmaceutical preparation, such as concrete setting, epoxy hardening, biological fermentation, cooking, pasteurization, sterilization and the like, where the material needs to be properly cured, incubated, or heat treated before the material is fit to use. Since curing, incubation, or heat treatment processes are often temperature dependent, typically taking longer to proceed at lower temperatures, such materials must undergo a certain minimal time-temperature history before they are fit for use.
As a result, visual time-temperature indicators are widely used in many areas of commerce. These are typically small devices that are affixed to a container of thermally sensitive material. For example, visual time-temperature indicators are often used to verify that a perishable, temperature sensitive product has been transported from the manufacturer to the user via a transport process that has preserved the “cold chain”. Here, a “cold chain” means a continuous system for conserving and preserving materials at precise temperature or within a range of temperatures from production to use, so that the integrity of the materials is assured.
One type of time-temperature device relied on a chemical reaction that mimics the degradation of the product to which attached. Another type of time-temperature device merely records the temperature profile for later output, with no other functionality. One drawback of such devices is that such devices may not be reusable. Rather, the device is used once and discarded. This can be expensive. Another drawback of such devices is that the devices are typically not accurate. For example, known visual temperature indicators which are chemically mediated give immediate visual results, but are not particularly accurate. These chemical indicators attempt to mimic the degradation characteristics of a material of interest by finding a different sensor material chemical with complementary degradation characteristics, such that observations of the change in the sensor material correspond to alterations in the material of interest. The drawback of this chemical approach, however, is that most materials of interest, such as biological materials, often may have unique and complex time-temperature profiles. In particular some materials may have time-temperature degradation characteristics that differ profoundly from simple exponential (Arrhenius profile) degradation rates. By contrast, however, there are only a limited number of sensor chemicals that are suitable for visual time-temperature indicators. It is often difficult or impossible to find an exact match, over all temperatures, between the degradation rate of the sensor chemical, and the degradation rate of the material of interest. As a result of these matching problems, the present practice is to be conservative. That is, chemical time-temperature indicators are usually set to degrade more quickly than the material of interest. Although this scenario will insure that the user does not inadvertently accept degraded material, it is inefficient. In many case, material that is, in fact, still good may be inappropriately discarded due to poor time-temperature indicator accuracy. Of course, the alternative scenario, in which the chemical time-temperature indicator fails to adequately warn that the tracked material is degraded, is both unacceptable and potentially dangerous. A further drawback of such devices is that they are prone to tampering. Particularly, unless the device has a unique ID, a device indicating that an adverse condition has occurred can easily be swapped with a new device reflecting no adverse condition. To avoid tampering, the device can be placed inside the packaging of the products to be monitored. However, the device is then not visually accessible until the package is opened.
Another type of non-visual time-temperature device is an RFID tag that records a temperature profile. However, such tags require RFID interrogator to query the tags in order to extract the profile. Thus, a user may not be readily able to analyze the temperature profile unless he or she has an interrogator present. In the past-paced world of supply chain operations, by the time the user is able to scan the tag for the data, he may have already accepted spoiled goods.
There is therefore a need for a device that is capable of providing both a visual or tactile indication of occurrence of a predetermined condition as well as an electronic indication of the occurrence of the condition, and which overcomes the drawbacks mentioned above.